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3. Ponding on roof by constricted downspouts <br />a) Advantages <br />_. Runoff delay and/or retention. <br />Cooling effect for building. <br />-Fire protection for building (roof water <br />may be trapped in case of fire). <br />b) Disadvantages <br />higher structural loadings. <br />--Clogging of constricted downspout requires <br />maintenance. <br />Freezing during winter. <br />-Waves and wave loading. <br />Leakage of roof water into building. <br />c) Applicability <br />Applies mainly for large office and commer- <br />cial type buildings, and institutional buildings. <br />-4. Increased roof roughness with rippled roof or gravel <br />on roof <br />a) Advantages <br />-Runoff delay and some reduction (detention <br />in ripples or gravel). <br />b) Disadvantages <br />-Somewhat higher structural loadings. <br />c) Applicability <br />Applies to flat roofs. <br />5. Groundwater recharge by perforated pipe or hose, <br />French drain, porous pipe, dry well <br />a) Advantages <br />---Runoff reduction (infiltration is increased; <br />some storage can be provided). <br />--Groundwater recharge with relatively clean <br />water. <br />-Little evaporations loss. <br />-May supply wager b garden or dry areas. <br />